Scanning probe microscope

ABSTRACT

Features for incorporation with scanning probe microscopes are provided which may be used separately or together. The features include constructing the microscope with a hinged top housing providing easy access to the heart of the microscope; a self-aligning and torque limiting magnetic clutch coupling a motor drive powering at least one vertical adjustment screw of the microscope; a removable microscope head for easy adjustment; an optical microscope, optionally mounted to an electronic camera and imaging system, installed adjacent to the head; operation on an inverted microscope stage; bowing error correction; a gas sparging system providing contaminant and noise reduction; a glove box type of loading system so that reactive materials may be safely loaded into the microscope; and a compact desk-top chamber which provides acoustic and vibration isolation.

CROSS-REFERENCE TO RELATED APPLICATION

This is a division of application Ser. No. 08/653,200 filed May 24, 1996now U.S. Pat. No. 5,675,154, which is a continuation-in-part of Ser. No.08/388,068 filed Feb. 10, 1995 and entitled "Scanning Probe MicroscopeFor Use in Fluids", in the name of the same inventors and assigned tothe same entity. It is hereby incorporated herein by reference as if setforth fully herein.

BACKGROUND OF THE INVENTION

This invention relates to scanning probe microscopes, such as thescanning tunneling microscope (STM) and atomic force microscope (AFM),used for profiling the surface of a sample at high resolution. Moreparticularly, the present invention relates to scanning probe microscopeapparatus having a hinged motor drive apparatus, video opticalmicroscope, bow correction, a desk-top isolation chamber, a gas spargingsystem and/or a glove box loading system.

Scanning probe microscopes make use of a fine probe tip which is scannedover the surface of a sample in order to record the topography of thesurface by means of the interaction between the probe tip and a sample.A typical layout of an atomic force microscope 10 is shown in FIG. 1.Here, the sample surface 12 of sample 14 is sandwiched between a topsensing assembly 16 and a bottom scanning assembly 18. Sensing assembly16 contains a laser 20 which emits a beam 22 that is reflected off ofthe back of a flexible cantilever assembly 24 to generate a reflectedbeam 26. Small motions of cantilever 28 of cantilever assembly 24modulate the position of beam 26 and are detected by a positionsensitive detector 30 which may be a bi-cell, multi-cell, or other typeof light beam position sensitive measuring device. Scanning of thesample surface 12 is achieved by a piezo-electric transducer or"scanner" 32 which moves the sample both up and down (i.e., towards andaway from flexible cantilever assembly 24 in the "Z" axial direction)and side to side in the "X-Y" planar direction (normal to the Z-axis),so as to generate a raster-scan of sample surface 12 under thecantilever 28. Scanner 32 is attached to a base 34 and positioning screwdrives 36, 38 are used to position top sensing assembly 16 so thatcantilever 28 is close to sample surface 12.

While fit for its intended purpose, the foregoing arrangement suffersfrom a number of drawbacks, most notably the fact that the sample 14must be sandwiched between bottom scanning assembly 18 and top sensingassembly 16. Access to sample 14 is therefore restricted, so that theuse of an optical microscope to examine sample 14 while in position onscanner 32 is made difficult. Sample mounting is also somewhat complexas is sample translation. It is desirable to be able to examine thescanning probe with an optical microscope as an aid to alignment oflaser beam 22 onto the cantilever while the sample 14 and cantilever 24are in place. In the past, this has been achieved by clearing a path forviewing as illustrated in FIG. 2. In FIG. 2, the incident laser beam 40is now incident from one side, and deflected down onto the cantilever 42by a beam-splitter 42 which is mounted on an optical window 44. Thereflected beam 46 from the back 48 of cantilever 42 is picked off by amirror 50 which transmits reflected beam 52 to the detector (not shownin FIG. 2, but disposed along the path of beam 52). Along-working-distance objective 54 of an optical microscope 56 is placedover the top of optical window 44 and focused onto the back 48 ofcantilever 42. This arrangement requires that the scanning probemicroscope be situated at the position normally occupied by the opticalmicroscope stage. This requires the use of an optical microscopeconsiderably larger than the scanning probe microscope itself. Inaddition, the whole assembly must then be set on a large table locatedso that an operator can have access to the eyepieces of the opticalmicroscope. Since vibration isolation is required for high resolutionscanning probe microscopy, an expensive and cumbersome air-table isusually required for optimum results.

It is often desirable to observe the sample from below while it isscanned from above. This may be done if the sample is transparent byplacing the scanning assembly on the optical stage of an invertedoptical microscope. An example of such an arrangement is the BioScope™available from Digital Instruments, Inc. of Santa Barbara, Calif. It isshown schematically in FIG. 3. A massive frame 58 holds a scanning probeassembly 60 with a probe 62 lowered down onto the sample 64 which is onthe stage 66 of an inverted optical microscope 68, the objective lens ofwhich is shown as 70. The detector 72 for reflected light 74 from laserbeam 76 is held off to one side of the probe assembly 60 and both arerigidly attached to a rigid and massive frame 58 which is also rigidlyattached to the inverted optical microscope stage 66. Once again, alarge support such as an air table is required to support the wholeassembly in order to achieve optimum results.

Many of the problems associated with the conventional scanning probemicroscope of FIG. 1 were solved by an invention disclosed by S. M.Lindsay and T. Jing in U.S. patent application Ser. No. 08/388,068entitled: "Scanning Probe Microscope for Use in Fluids". The scanningprobe microscope arrangement of the above-identified disclosure isillustrated generally in FIG. 4. Here, a single microscope body 78 holdsboth mechanical vertical tripod adjustments 80, 82 and 84 and samplestage 86 which is held on to the bottom of the mechanical adjustments bymagnetic balls, two of which are shown at 88 and 90. The scanningassembly 92 scans either an STM probe or an AFM probe over the surfaceof a sample which is attached to the upper surface 94 of sample stage86. In this way, the sample may be accessed from below. A containmentmay be used to surround the sample so as to control the sampleenvironment. A motor 96 which drives at least one of the mechanicaladjustments 80, 82, 84 (here, 80) is housed on an assembly 98 which isseated on top of the microscope body 78. Motor 96 is coupled tomechanical adjustment 80 which may be a screw driven by a sleeve 100which permits translation of the screw 80 as it is rotated. In order togain access to the other adjustments 82, 84, it is necessary to have anopening 102 in the housing 104. Even so, it can be difficult to makeadjustments to the scanning assembly 92.

In order to realize this top-down scanning arrangement for the AFM, atracking method is required so that the laser beam remains aligned onthe force sensing cantilever as it is moved over the surface of thesample. Such an arrangement has been achieved by a prior inventiondisclosed by P. S. Jung and D. R. Yaniv in U.S. Pat. No. 5,440,920,hereby incorporated herein by reference. A general arrangement of thisoptical tracking scheme is shown in FIG. 5A. A lens 106 is used to focusa collimated beam 108 from a laser (not shown) onto the reflective back110 of a cantilever-type probe 112. Both the lens 106 and thecantilever-type probe 112 are physically coupled to or constrained tomove with the scanning transducer 114. In this way, a focused laser spotfrom beam 108 tracks and follows cantilever 112 as it is moved over thesurface of the sample. This action is illustrated in FIG. 5B. Thetransducer 114 is bent so as to move the tip 116 of probe 112 to a newposition. Lens 106 has been translated with scanning transducer 114, sothat the focused laser spot remains on the back 110 of the cantilever112.

FIG. 5B illustrates a problem associated with this method of trackingthe incident beam with the cantilever. It does not compensate for theangular deflection of the cantilever due to the bending of the scanner.Since this angular deflection adds or subtracts from the angulardeflection whereby changes in height of a scanned sample are detected,it introduces an error in the output signal of the detector which causesa flat surface to appear to be curved or "bowed". When the microscope isscanning a sample, this bow can become quite complicated. For example,if the cantilever probe is in contact with the sample surface andadhering to it, when the transducer is pushed forward and up in order tolift the cantilever from the surface (as shown in FIG. 6A) themicroscope can become unstable because the cantilever will jump from thesurface when the force pulling it up becomes comparable to the adhesionforce. Furthermore, the direction of the bowing error is difficult topredict because it depends upon the location of the laser spot on thecantilever. The bowing is more predictable in the opposite scandirection where (as shown in FIG. 6B) the tip tends to be pushed intothe surface. The tip is also more stable in this configuration, but, fora given deflection of the laser beam, the contact force between theprobe and the sample is significantly increased as the tip is pushedinto the surface. This is a disadvantage when scanning soft surfaces.U.S. Pat. No. 5,440,920, discussed above, describes a solution to thisproblem using an "S"-shaped scanner. According to this arrangement, apair of scanning tubes are connected together in a manner which resultsin translation without angular deflection. However, this arrangement maynot always be desirable because it requires a longer scanning tube whichcan result in the introduction of more mechanical drift and noise in thesystem.

OBJECTS AND ADVANTAGES OF THE INVENTION

Accordingly, it is an object of the present invention to provide ascanning probe microscope in which an adjustment motor is placed abovethe scanning stage in a manner which permits easy access to the scanningstage for adjustments.

It is a further object of the present invention to provide a magneticclutch for coupling a motor controlling an adjustable leg which in turnsupports a sample platen of a scanning probe microscope.

It is a further object of the present invention to provide a microscopein which optical access is available so that the position of the laserspot on the back of the cantilever is easily imaged by an opticalmicroscope to aid alignment of the microscope.

It is another object of the present invention to provide a televisioncamera or similar imaging device in the optical path from the back ofthe atomic force microscope cantilever in order to provide electronicimages of the position of the light beam of the back of the cantilever.

It is yet another object of the present invention to provide amicroscope that can also be placed onto the stage of an inverted opticalmicroscope so that an optically transparent sample being scanned may beviewed from below.

It is yet another object of the present invention to reduce or eliminatebowing errors without the need of a large increase in the total scannerlength for a given scanning range.

It is yet another object of the present invention to provide a glove boxtype of loading system for a scanning probe microscope.

It is yet another object of the present invention to provide a gassparging system for use with a scanning probe microscope.

It is yet another object of the present invention to provide aconvenient, desk-top anti-vibration and acoustic isolation system.

These and many other objects and advantages of the present inventionwill become apparent to those of ordinary skill in the art from aconsideration of the drawings and ensuing description of the invention.

SUMMARY OF THE INVENTION

Features for incorporation with scanning probe microscopes are providedwhich may be used separately or together. The features includeconstructing the microscope with a hinged top housing providing easyaccess to the heart of the microscope; a self-aligning and torquelimiting magnetic clutch coupling a motor drive powering at least onevertical adjustment screw of the microscope; a removable microscope headfor easy adjustment; an optical microscope, optionally mounted to anelectronic camera and imaging system, installed adjacent to the head;operation on an inverted microscope stage; bowing error correction; agas sparging system providing contaminant and noise reduction; a glovebox type of loading system so that reactive materials may be safelyloaded into the microscope; and a compact desk-top chamber whichprovides acoustic and vibration isolation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a typical arrangement of an atomic force microscopeaccording to the prior art.

FIG. 2 shows an arrangement for optical microscope access to the back ofa scanning cantilever-type probe according to the prior art.

FIG. 3 shows a scanning probe microscope for use on an inverted opticalmicroscope according to the prior art.

FIG. 4 shows the arrangement of a scanning probe microscope with theadjustment screws and motor mounted above the sample.

FIGS. 5A and 5B show an optical tracking system according to the priorart whereby the laser spot remains focused on the cantilever as it isscanned over the sample. FIG. 5A shows the scanning tube prior todeflection and FIG. 5B shows the scanning tube after deflection.

FIGS. 6A and 6B shows deformations of the cantilever during scanningwhich give rise to bowing error. FIG. 6A shows the deformation when thetransducer swings up so as to lift the cantilever from the surface. FIG.6B shows the deformation when the transducer pulls back so as to pushthe transducer into the surface.

FIG. 7 shows a general layout of the scanning probe microscope accordingto a presently preferred embodiment of the present invention.

FIG. 8 shows the microscope of the present invention with the head swungback to disengage the motor and expose the scanning head according to apreferred embodiment of the present invention.

FIG. 9 shows the magnetic clutch and drive-sleeve which releasablycouple the motor to the adjustment screw according to a preferredembodiment of the present invention.

FIG. 9A is a cross sectional view taken along line 9A--9A of FIG. 9.

FIG. 9B is a cross sectional view taken along line 9B--9B of FIG. 9.

FIG. 9C is a cross sectional view taken along line 9C--9C of FIG. 9.

FIG. 10 shows the placement of a video microscope for viewing the backof a cantilever-type probe in a scanning probe microscope according to apresently preferred embodiment of the present invention.

FIG. 11 is a side view showing the optical train used in the videomicroscope portion of a scanning probe microscope according to apresently preferred embodiment of the present invention.

FIG. 12 is a top plan view taken along line 12--12 of FIG. 11 of thefront of the optical train used in the video microscope portion of ascanning probe microscope according to a presently preferred embodimentof the present invention.

FIG. 13 is a cross-sectional side view of the microscope placement on aninverted optical microscope stage in a scanning probe microscopeaccording to a presently preferred embodiment of the present invention.

FIG. 14 shows the relationship of a scan direction (chosen to be the "Y"axis here) to the deflection signal generated by cantilever distortionsdue to the angular swing of the scanner in a scanning probe microscopeaccording to a presently preferred embodiment of the present invention.

FIG. 15 shows an electronic circuit for compensating for bow so thatcontact force is not increased in a scanning probe microscope accordingto a presently preferred embodiment of the present invention.

FIG. 16A is a cross-sectional diagram of a bow-compensating scanneraccording to a presently preferred embodiment of the present invention.

FIG. 16B is a side view of a bow-compensating scanner according to apresently preferred embodiment of the present invention.

FIG. 16C is a top view of a bow-compensating scanner according to apresently preferred embodiment of the present invention.

FIG. 16D is a side view of a bow-corrected scanning probe microscopeutilizing a pair of cooperating piezoelectric cylinders according to apresently preferred embodiment of the present invention.

FIG. 17 shows a desk-top vibration and acoustic-noise isolation chamberfor use with a scanning probe microscope according to a presentlypreferred embodiment of the present invention.

FIG. 18 shows a gas sparging system for a scanning probe microscopeaccording to a presently preferred embodiment of the present invention.

FIG. 19 shows an Atomic Force Microscope detector fine adjustmentapparatus according to a presently preferred embodiment of the presentinvention.

FIG. 20 shows an alternate view of an Atomic Force Microscope detectorfine adjustment apparatus according to a presently preferred embodimentof the present invention.

FIG. 21 shows a perspective view of a glove box loading system accordingto a presently preferred embodiment of the present invention.

FIG. 22 is a side elevational view of a portion of the glove box loadingsystem according to a presently preferred embodiment of the presentinvention.

FIG. 23 shows an adjustable sample platen with adjustable kinematicmounts.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Those of ordinary skill in the art will realize that the followingdescription of the present invention is illustrative only and is notintended to be in any way limiting. Other embodiments of the inventionwill readily suggest themselves to such skilled persons from anexamination of the within disclosure.

Hinged Head Assembly and Magnetic Clutch Mechanism

Turning now to FIG. 7, a side elevation view of the scanning probemicroscope having a hinged housing according to a presently preferredembodiment of the present invention is shown. The microscope body 118rests on a supporting base 120 which may also preferably serve as ahermetically sealed sample enclosure. The sample stage 122 is fabricatedfrom material that is attracted to magnets and is held in place on threemagnetic balls, two of which are shown as 124 and 126, which are affixedto the end of mechanical linear positioners, such as screw drives 128,130 and 132. The scanning probe 134 protrudes into the area above samplestage 122. One of the mechanical linear positioners, 132, is a screwcoupled to a motor 136 driven in order to permit automated advance ofthe sample on sample stage 122 towards the scanning probe 134. The motor136 is coupled to screw 132 by a coupling sleeve 138 that is free toride up and down on the shaft of screw 132, but grips it for rotationalmotion as shown in more detail in FIG. 9. The coupling sleeve 138 iscoupled to the motor drive shaft 140 by a self-aligning magnetic clutchassembly 142 (shown in more detail in FIG. 9). The motor, 136 is mountedon a head assembly 144. The head assembly 144 is connected, at one pointon its circumference, by a hinge 146 which permits the head assembly 144to swing back with respect to the microscope body 118. An opening 148 inhead assembly 144 permits access to the inside of head assembly 144 whenhead assembly 144 is in the down or closed position shown in FIG. 7,allowing the operator to view probe 134 via a window in the scanningassembly 150 either directly or with an optical microscope.

The head assembly 144, as open and swung back for access to thealignment screws 128, 130, is shown in FIG. 8. The head assembly 144rests on the hinge assembly 146 which is, in turn, connected to the body118 of the microscope. While the head assembly 144 is open, the magneticclutch 142 is disengaged so that its bottom part 138 rests on screw 132while its top part 140 remains attached to motor 136. The bottom element152 of hinge assembly 146 is shaped so that the top element 154 of hingeassembly 146 comes to rest on it with the microscope head assembly 144pulled back at a convenient angle as shown in FIG. 8. By these means,easy access is gained to the adjustment screws 128 and 130 and thescanner assembly 150 by the simple expedient of pulling the headassembly 144 back. When the head assembly 144 is closed against the body118, the magnetic clutch engages and self-aligns, so that the microscopeis immediately ready for operation. The head assembly 144 is preferablyretained in its (normal) closed position by spring-loaded pins (notshown) which are pushed in (or released) by the operator in order toswing the head back for access.

The arrangement of the magnetic clutch 142 is shown in more detail inFIG. 9. The sleeve or bottom part 138 of the clutch 142 rides on motordriven adjustment screw 132 and is capable of translation up and downwhile still grasping the screw 132 for rotation. This is because anon-circular and/or keyed cross-section is used for this sleeve 138 asshown, for example, at 156 where sleeve 138 surrounds hexagonaladjustment screw 132 as shown so that up-down motion is permitted, butnot relative rotational motion. More detail of the magnetic clutch 142is shown at 158 and 160. Four magnets 162, 164, 166, 168 are preferablymounted in the top of the motor drive shaft 140. Similarly, four matingmagnets 170, 172, 174, 176 are mounted in the top of sleeve 138 asshown. The magnets may be mounted with all north poles projectingdownward from motor drive shaft 142 and all south poles projectingupwardly from sleeve 138 so that simple engagement may be achieved every90 degrees. Alternatively, a different keying scheme may be used so thatonly one orientation is possible is such an arrangement is desired, forexample, 3 norths and a south from the top could mate with 3 souths anda north from the bottom so that engagement between parts 138 and 140could only occur in one angular orientation. Used with small rare-earthdisk magnets (e.g., 3/16" diameter) this arrangement gives ample forceto pull the sleeve up into position from as much as a centimeter andample torque to drive the adjustment screw 132. Yet it offers verylittle resistance when the head is tilted back. Thus, the motor assemblyis automatically disconnected and reconnected each time the head istilted away and back again without the need for any complicatedmechanical connection/disconnection.

Optical Train

An optical microscope 178 which allows the top of the AFM cantilever ofthe scanning probe to be monitored during alignment and scanning isshown in FIGS. 10 and 11. FIG. 10 shows the overall arrangement ofoptical microscope 178 in relation to the scanning probe microscope 180.The optical microscope assembly 178 is mounted onto the scanning probemicroscope body 118. The front part 182 of the optical microscope 178passes through an opening 184 in scanner assembly 150 so that a view ofthe scanning cantilever is possible. The opening 148 allows the headassembly 144 to swing back to the open state while the opticalmicroscope 178 remains attached to the scanning probe microscope body118.

The optical train or path of the scanning probe microscope AFM head isshown in FIG. 11. This figure shows the optical train used for sensingdeflection of cantilever 186, so that the relationship between the twooptical systems is clear. A collimated laser beam 188 from a laser (notshown in FIG. 11) passes through a converging lens 190 attached toscanner 192 preferably at or near its bottom 194. Beam 188 is focuseddown onto the back 194 of cantilever 186 which is held in the glassblock 196 attached to the bottom 194 of scanner 192. The reflected beam198 from the back 194 of cantilever 186 is incident on positionsensitive detector 200. The optical microscope 178 is arranged so as toview the back portion 194 of cantilever 186 as illuminated by theincident beam 188 of the laser. A small mirror 202 is set to one side ofand just above position sensitive detector 200 so as to collect somelight from the back 194 of cantilever 186. This arrangement isillustrated in a top plan view in FIG. 12 as taken along line 12--12 ofFIG. 11. The laser spot 204 is seen on the back 194 of cantilever 186 inthis view. Mirror 202 sits off to one side of the detector 200 (thedetector is situated above the laser spot and not shown in FIG. 12).Diffuse light from the back 194 of cantilever 186 is passed to a firstlens 206. Returning to the side view (FIG. 11), first lens 206, secondlens 208 and bending mirror 210 form an image of the back 194 ofcantilever 186 on the image plane of a charge coupled device (CCD)camera 212. The long-working distance required by the lens assembly oflenses 206 and 208 (typically 40 mm) limits the magnification of thesystem to 5 or 10 times if the distance to the camera 212 is not to beunwieldy. However, this is adequate to fill the sensitive area of a CCDimaging chip (approximately a 1 mm by 1 mm square) with a view of thecantilever back 194 (approximately a 0.1 mm by 0.1 mm image area). Theremainder of the magnification is purely electronic and results from theprojection of the CCD image from camera 212 onto a TV monitor (notshown).

In another embodiment of the system, shown in FIG. 13, the microscope220 may be placed on the optical stage 222 of an inverted microscope 224so that the scanning of a transparent sample may be viewed from below.This is achieved using the free-standing mode of operation of themicroscope as described in U.S. patent application Ser. No. 08/388,068,referred to above. The sample stage has been removed so that themagnetic balls, two of which are shown at 226, 228, now ride on theglass stage 222 of an inverted optical microscope 224. The objectivelens 230 of the inverted optical microscope 224 is focused through atransparent sample container or substrate 232 onto the region scanned bythe scanning probe 234. The position of the microscope 220 on samplestage 222 of optical microscope 224 is adjusted by means of micrometerscrews (not shown) which translate the whole assembly 220 over thesurface of the glass plate 220 of the optical stage of the invertedmicroscope 224. These optical stages are normally rigid and smooth, andform an ideal surface for moving the microscope over.

Bow Error Correction and Reduction

The bow-correction system useable with the scanning probe microscopehereinbefore described is illustrated in FIGS. 14 and 15. The geometryof the top-down scanner 240 is illustrated in FIG. 14. The collimatedlaser beam 242 from a laser light source (not shown in FIG. 14) isfocused onto the back 244 of a cantilever probe 246 by a converging lens248. Both the lens 248 and cantilever 246 are preferably attached to thebottom (or near the bottom) of a scanner element 250. The reflected beam252 falls onto a position sensitive detector 254. Detector 254 isarranged to sense vertical movement of the cantilever by means of thearrangement of two segments 256 (A) and 258 (B). Segments 256 and 258are positioned so that if the cantilever 246 moves up, then more lightis reflected onto segment 256. Segment 256 produces an output signal Aand segment 258 produces an output signal B. The deflection signal isobtained from the difference between the signals from the two segments,A-B divided by their sum A+B so that the deflection signal isindependent of the absolute magnitude of the laser signal, reflection,etc. In FIG. 14, movement of the probe is defined in the directionformed by the intersection of the plane of the beams 242 and 252 and thesample surface plane as movement in the y direction. Movement in theperpendicular direction in the plane of the sample surface is in the xdirection. Bow is caused by the fact that the scanner 250 does notremain on a fixed plane, but introduces vertical motion and angulardeflection as the scanner tube is bent in order to scan. Bow in the xdirection will not affect the signal (A-B)/(A+B) unless the unwanteddeflection is so large that it causes the reflected beam 252 to missdetector 254 entirely. Bow caused by the y scan does introduceundesirable signal, and, as shown earlier, it has the effect of causingthe cantilever 246 to be pushed down into the surface being scanned whenthe scan is away from the detector and to be pulled up from it when thescan is towards the detector. This is the result of the action of thefeedback control system used with scanning probe microscopes and wellknown to those of skill in the art which moves the scanner up and downin an attempt to keep the deflection signal constant. Pulling up canhave the undesirable effect of causing cantilever 246 to lift-off thesurface being scanned, but this only happens at large angularexcursions, so the effect is easily minimized by using a relatively longscanning tube. Pushing down into the surface is always undesirablebecause it increases the tracking force used in the microscope and thisdisrupts soft surfaces such as biological materials which it isdesirable to be able to scan. However, this error is approximatelylinear as a function of scan voltage. It can be corrected for by addinga voltage proportional to the scan voltage to the deflection signal insuch a sense as to cause the scanner to lift up in just an amount tocompensate for the pushing-down that would occur otherwise. This is donewith the circuit shown in FIG. 15. A fraction of the y-scan voltage(denoted signal "y") is set by the resistive divider comprisingresistors R1 and R2. In one direction of scan (the y sweep away from thedetector), this signal is subtracted from the deflection signal A-B/A+Busing operational amplifier 260. In the other direction of scan (wherethe y scan polarity is reversed and the cantilever sweeps towards thedetector) the signal is shorted out by the diode D1 and no correction isapplied. The ratio, R1/R2, depends upon the sensitivity of the scannerelement 250. This design of correction circuit can accommodate differentscanners through the simple expedient of placing R2 (for example) in thescanner body, so that, as the scanner is changed, so is the value of R2.Similarly, a variable resistor could also be used and set in any of anumber of ways well known to those of ordinary skill in the art.

Alternatively, the bow can be corrected by use of a novel scannerarrangement as described below. This novel scanner has the advantage ofeliminating the lift-off of the cantilever when a large displacement ismade in the direction that lifts the cantilever (as shown in FIG. 6A).The distortion of the cantilever due to bow is determined by the angleformed by the bending of the scanning tube in the y direction (asdefined in FIG. 14). P. S. Jung and D. R. Yaniv, supra, and Elings etal., in U.S. Pat. No. 5,306,919, describe a scheme for removing angulardisplacements of the cantilever of a scanning probe microscope by usingtwo equal and opposite angular deflections of a long tube, so that thetotal displacement describes an "S"-like shape, the end of the tubebeing translated but not subject to angular deflection. As previouslystated, this scheme requires the use of a substantially increased lengthof scanning tube for a given range of scan. While fit for its intendedpurpose, this configuration is both electrically and mechanically morenoisy than a shorter tube. Since, however, it is correction of theangular deflection that is required, it is not necessary to use tubes ofequal dimension to achieve the benefits of the device described by Junget al. and Elings et al. Elings et al., in another approach described inU.S. Pat. No. 4,871,938, describe an STM system where the tip is placedon one side of the tube at its circumference and that side is deflectedso as to compensate for the angular deflection. However, while fit forits intended purpose, this arrangement results in a substantialreduction of the scan range available from a given tube employing theinvention herein.

The same corrective effect can be obtained by using a much shorteropposing deflection, but by applying it across a much shorter distance,so that the total angular correction is the same as would be obtainedwith a longer tube bent over a longer distance. A scanner 270 accordingto this invention is shown in FIG. 16A in cross section. A side view isshown in FIG. 16B and a top view is shown in FIG. 16C. In a conventionalscanner, there are four electrodes disposed along the length of thescanner tube. These are generally denoted, travelling about thecircumference in clockwise fashion, +Y, +X, -Y, and -X. The +X electrodeis opposite the -X electrode and the +Y electrode is opposite the -Yelectrode. The +X and -X segments are connected to voltages of oppositepolarity so that as one side of the tube is expanded in response to theapplication of a positive voltage, the other side will contract due toapplication of a negative voltage. The net effect is that the tube bendsin a controlled manner in response to the application of voltages.

According to a presently preferred embodiment of the present invention,a short segment 272 of the +Y electrode 274 is isolated to form aseparate electrode and that electrode is powered by the -Y voltagesupply. Thus the lower portion of the scanning tube on the +Y side isdeflected in a direction opposite to the remainder of the tube on the +Yside. If the length of opposing electrode 272 is less than half thetotal length of the scanner tube 270, then the opposing angulardeflection is less than that needed to compensate for the angulardeflection caused by the upper part of the tube. If however, the small,opposing displacement from opposing electrode 272 is applied across adistance much less than the diameter of the scanner tube 270, a largercompensating angular deflection can be generated. According to apresently preferred embodiment of the present invention, cantileverprobe assembly 276 is mounted on a rocking block 278 held in place on awedge-shaped fulcrum 280 and a ball 282 by the action of a magnet 284that pulls rocking block 278 up against ferromagnetic material 286 onthe end of scanner 270. The distance "d" between fulcrum 280 and ball282 is chosen such that the angular deflection due to the opposingelectrode 272 is equal in magnitude (but opposite in sign) to theangular deflection produced in the y direction by the rest of the tube.

It is to be appreciated that ball 282 can be fabricated of a magnet andattached to block 278, thus obviating the need for magnet 284,similarly, portion 286 could be fabricated of a magnet, ball 282 of amaterial attracted to magnets, and magnet 284 obviated. Other similararrangements will appear to those of ordinary skill in the art.

Another embodiment of a bow-correction system is shown in FIG. 16D. Thisversion uses two small piezoelectric cylinders, shown as 288a and 288bin FIG. 16D. Each cylinder has an outer and an inner electrode surfaceallowing it to be expanded or contracted in vertical length. One end ofeach cylinder is rigidly attached to a housing 290 which is in turn,rigidly attached to the free end of the main scanning tube 292. Thelower ends of the tubes 288a and 288b are rigidly attached to acantilever housing 294 to which the force sensing cantilever 296 is, inturn, attached. The required angular displacement is obtained bycontracting one tube (e.g., 288a) and expanding the other (e.g., 288b).The deflection signal is somewhat reduced because of the stiffness ofthe mounting elements (i.e., the tubes 288a and 288b) but thisarrangement has the advantage of increased mechanical stability. Onceagain, by placing two small tubes close together, an adequate angulardeflection can be obtained, without the disadvantage of a reduced scanrange as in the prior art. The control of the signals necessary toaccomplish this can be supplied by a power supply under the control of acomputer as well known to those of ordinary skill in the art.

Scanning probe microscopes usually require vibration isolation and it iscommon to do this by setting them on a heavy slab mounted on elasticcords or springs. Another approach is to use an air-table. Although theair-table generally functions less well than a slab on springs, it iscommonly used because of its ability to keep the microscope at aconvenient height for the operator. It is usually necessary to providesome additional isolation to keep out acoustic noise (such as a heavybox placed over the whole system). It is, however, possible to optimizethe parameters of slab and spring system so that the displacement causedby putting the microscope on the isolation stage is small and acousticisolation is straightforward. Such an isolation system is shown in FIG.17. An acoustic isolation box 300 is used as the support for a vibrationisolation system within the box 300. Box 300 is shown with its accessdoor 302 open. The vibration isolation system consists of elastic cords304, 306, 308 and a forth cord hidden by the wall of the box 300suspending a massive slab 310. Such suspensions have usually beenassembled as large systems (e.g., suspended from a ceiling). However,the only requirement is that the system has a low resonant frequency,typically 1 Hz for longitudinal vibrations. If the slab 310 (plusmicroscope) extend the elastic cords 304, 306, 308 and the hidden one,by an amount x, then it follows from elementary mechanics that theresonant frequency, f, of the assembly is: ##EQU1## where g is theacceleration due to gravity. Thus, a resonant frequency of 1 Hz isobtained for an extension (x) of 25 cm, independent of the size of theisolation system. By using stiff cords 304, 306, 308, etc. and a verymassive slab 310, a small system can be built. This approach also hasthe advantage that the extra movement caused by putting the microscopeonto the slab 310 is small (because the fractional added mass is small).So, if the slab is near desk height to begin with, it moves only alittle when the microscope is placed onto it. One successful embodimentused four commonly available 1/4" diameter bungee cords to hold a 60pound lead-loaded slab. The height of the whole enclosure is only 3' andit sits conveniently on a desk top. By building the enclosure from adense material with a well-fitting door, excellent acoustic isolation isalso obtained. A microscope operated in this desk-top enclosure givesatomic resolution routinely in high ambient noise environments.

Gas Sparging System

The inventors have discovered that it is often desirable to removedissolved gasses, particularly oxygen, from solutions used in a scanningprobe microscope. This is because the chemical reactivity of oxygenlimits the range of electrochemical potential that can be used andlimits the nature of the compounds that can be studied in themicroscope. A somewhat similar problem arises in liquid chromatographyand it has been described in detail by Bakalyar et al. S. R. Bakalyar,M. P. T. Bradley and R. Honganen, Journal of Chromatography, 158,277-293 (1978)!. These workers found that sparging (bubbling a gasthrough) the solution with helium effectively removed all the dissolvedoxygen. Helium has a very low solubility in most solvents, so that itnot only replaces the undesired gas, but is less likely to form bubblesthan other gasses with a higher solubility.

The present design of the microscope lends itself to sparging of theliquid sample by gasses. FIG. 18 shows a presently preferred embodimentof the present invention employing a gas sparging system. The samplecell 312 situated on the sample platen 314 is in place in thehermetically sealed sample chamber 316 of the microscope. Inert gas maybe passed directly into the liquid 318 in cell 312 for degassing bysparging using one of the liquid input lines 320 previously described inU.S. patent application Ser. No. 08/388,068, discussed supra. Inert gasis also preferably passed into the body of the chamber 316 via an inlet322. An outlet 324 permits flow of the gas through the system. Thedirect sparging of the sample cell 312 is only required in order toaccelerate the initial degassing. Degassing will still occur (but moreslowly) so long as a flow is maintained through the chamber 316 such asis adequate to prevent the back-diffusion of air into the sample chamber316. Thus, in operation, gas may be flowed through inlet 322 and outlet324 initially, and the flow directly into the sample (via line 320)stopped and flow through the chamber maintained. The sample can thus bemaintained oxygen free without direct bubbling, avoiding mechanicalnoise during microscopy.

Nitrogen and argon both work well as sparging gasses, but helium has aparticular advantage. Because of its unusual acoustic properties (i.e.,its low density and thus, high speed of sound) it provides a pooracoustic impedance match to sound waves that originate in air (which ispredominantly nitrogen). Therefore, vibrations of the chamber wall 316caused by sound are less readily coupled into the chamber if it isfilled with helium. Thus, the helium serves a further purpose ofproviding acoustic isolation, improving the operation of the microscope.

AFM Detector Fine Adjustment

As described in U.S. patent application Ser. No. 08/388,068, discussedsupra, the AFM detector unit is aligned in one direction by sliding itin the slot on the microscope head and in the other (perpendicular)direction by rotating the entire AFM scanning assembly. Anotherembodiment of the detector unit which permits fine adjustment in thislatter direction is shown in FIGS. 19 and 20. This arrangement permits afurther (and finer) adjustment beyond that achieved by rotating thescanner head. In this alternative embodiment, the detector housing 326housing detector 325 is made narrower than the channel 328 that housesit by an amount "d" on each side. Housing 326 is held into channel 328by means of magnets 330 glued into the detector housing 326 and servingto hold housing 326 in the channel 328 (which is made of a magneticmaterial). A pin, 332 fixes one point of the housing 326 with respect tothe channel 328, so serving to define a rocking motion as indicated bythe curved arrow 334 in FIG. 19. The rocking motion is made by means ofa handle 336 inserted into the back of the detector housing 326. Lateralmotion Y1 of the handle is demagnified in the diminished motion Y2 ofthe detector. The demagnification ratio is set by the ratio of X1 (thedistance between the center of detector 325 and the center of pin 332)to X2 (the distance between the center of pin 332 and the end 338 ofhandle 336). In this way, fine adjustment of the lateral position of theAFM detector 325 is achieved.

Glove Box Loading System

The use of a hermetically-sealed housing for the microscope samplechamber as discussed in U.S. patent application Ser. No. 08/388,068,supra, permits reactive samples to be studied. However, it is oftendifficult to load such samples into the microscope chamber in the firstplace. If the entire microscope is placed into a sealed glove box, itmay be exposed to reactive chemicals. Furthermore, it would not bepossible to start sparging of the microscope sample chamber until afterthe microscope is passed out of the glove box and gas lines connected tothe sample chamber. An adapter which allows easy mating of themicroscope with a glove box is shown in FIGS. 21 and 22. Referring toFIG. 21, the microscope 340 seats against a plate 342 to form a hermeticseal. A glass chamber 344 may be attached to the bottom of the plate342. The plate 342 is bolted onto a glove box 346. Inert gas may bepassed through the glove box 346 by means of the gas supply lines 348,350. A similar pair of gas supply lines 352, 354 permits gas flowthrough the glass chamber 344 when it is in place. The gas supply lines348, 350, 352, 354 may be shut off by means of corresponding gas valves348a, 350a, 352a, 354a when not in use. A detailed section is shown inFIG. 22. The microscope body 340 is pushed into the plate 342 where itis retained by an O-ring 356. The plate 343 seats against the glove box346, to which it is affixed by bolts 358a, 358b. Magnets 360 pull amagnetic ring 362 up against the plate 342. The glass chamber 344 isaffixed to the magnetic ring 362. Thus, the glass chamber 344 may beeasily pushed into place and retained by the magnets 360.

The plate 342 is first bolted into place on the glove box 346 and themicroscope body 340 inserted into the plate 342. The gas supply lines352, 354 through plate 342 are sealed with valves 352a and 354a andinert gas flowed through the glove box 346 using the gas supply lines348 and 350 until the glove box 346 is purged of oxygen and otherundesired gasses and vapors. At this point, the sample can be prepared,placed on sample platen 364, and sample platen 364 mounted to themicroscope 340 in the inert atmosphere maintained by glove box 346. Oncethe sample platen 364 is mounted to microscope 340, the glass chamber344 may then be placed into position on the plate 342 and gas flowstarted through the gas supply lines 352, 354. The plate 342 may now beunbolted from the glove box 346 with the sample protected inside theglass chamber 344. The microscope, now resting on the glass chamber 344to which it is sealed, may now be placed into an enclosure for highresolution microscopy. With long gas lines 352, 354 connected to thechamber 344, this enclosure can be situated remotely from the glove box346 in operation. For low resolution microscopy, when acoustic isolationof the microscope is not so important, the microscope may be operatedin-situ in the glove box 346.

Sample Platen with Adjustable Kinematic Mounts

The sample platen described in U.S. patent application Ser. No.08/388,068, supra, is translated by means of adjustment pegs whichlocate in slots in the sample platen. However, it is sometimes desirableto be able to remove and replace the sample platen while retaining itsposition with respect to the microscope tip. For example, a very smallsample might be used and positioned with the use of an opticalmicroscope. It would be desirable to be able to remove and replace thesample platen with no loss of alignment. FIG. 23 shows an arrangementwhich permits this. The sample platen 366 mounts onto the magnetic ballsdisposed at the ends of threaded vertical adjustment rods by means ofthe cone 368 vee-groove 370 and plane bearings 372 which form a standardkinematic mount, allowing precise removal and replacement of the sampleplaten 366. In order to allow adjustment of the tip with respect to asample mounted on this platen 366, the vee groove 370 is madeadjustable. It is formed into a piece 374 which slides in a slot 376 inthe platen 366. The sliding piece 374 is locked into position by meansof two bolts 378, 380 which slide, respectively, in slots 382, 384. Inthe microscope, the tip is located over the sample in one direction ofmovement by sliding the vee-groove 370 in its slot 376. It is thenlocked into place with the bolts 378, 380. The perpendicular adjustmentis achieved by rotating the scanner in the body of the microscope.

Alternative Embodiments

Although illustrative presently preferred embodiments and applicationsof this invention are shown and described herein, many variations andmodifications are possible which remain within the concept, scope, andspirit of the invention, and these variations would become clear tothose of skill in the art after perusal of this application. Theinvention, therefore, is not to be limited except in the spirit of theappended claims.

What is claimed is:
 1. A scanning probe microscope comprising:a frame; aplurality of support members engaged with and extending from said frame;a positioning scanner attached to said frame; a sample stage suspendedfrom said support members; a scanning probe suspended from saidpositioning scanner and disposed in close proximity to said samplestage; and an optical microscope including an electronic camera disposedso as to project an image of said scanning probe to said electroniccamera.
 2. A scanning probe microscope according to claim 1 wherein saidoptical microscope is disposed below said sample stage and is arrangedto view said scanning probe through said sample stage.
 3. A scanningprobe microscope according to claim 2 wherein said electronic cameraincludes a charge coupled device array at its focal plane.
 4. A scanningprobe microscope according to claim 1 wherein said electronic cameraincludes a charge coupled device array at its focal plane.
 5. A scanningprobe microscope comprising:a frame; a plurality of support membersengaged with and extending from said frame; a positioning scannerattached to said frame; a sample stage including a transparent portionin contact with said support members; a scanning probe suspended fromsaid positioning scanner and disposed in close proximity to saidtransparent portion of sample stage; and an optical microscope includingan electronic camera disposed so as to project an image of said scanningprobe through said transparent portion of said sample stage to saidelectronic camera.